Physicochemical Degradation and Elemental Contamination of Marine Diesel Fuel During Storage and Handling Conditions

Abstract

The present study examines the physicochemical degradation and elemental contamination of marine distillate diesel fuels, which were stored in land-based tanks in operational conditions. Forty-one (41) samples, in compliance with ELOT ISO 8217:2024 were analyzed for crucial physicochemical properties. Stepwise regression identified magnesium (Mg) (positive) and chromium (Cr) (negative) as significant viscosity predictors (R2 = 0.269, p = 0.003, VIF < 2), while calcium (Ca), Phosphorus (P), zinc (Zn), copper (Cu), lead (Pb) and Ferrous (Fe) were excluded due to multicollinearity. Strong correlations (r > 0.85) between element pairs (Cu-Pb) (r = 0.996), Ca-Zn (r = 0.897), and P-Ca (r = 0.888) indicate common sources from lubricant additives (ZDDP) and brass corrosion, with individual correlations recorded for Ca (showing r = 0.679, p < 0.001), P (r = 0.722, p < 0.001), and Zn (r = 0.595, p < 0.001). The results revealed that fuels stored in carbon steel tanks under high-humidity conditions for over six (6) months recorded higher metal loads than those in stainless steel tanks with regular periodic supply. The FAME content in the studied samples ranged from 6.7 to 7.1% v/v and showed no significant correlation with degradation indicators (p > 0.05). The narrow FAME range examined precludes definitive conclusions regarding specific biodiesel effects. The threshold of 0.2 mg/kg, as set by manufacturers’ guidelines to protect injectors, was exceeded in the coastal carbon steel tank samples with eight (8) months of storage under high-humidity conditions and in the coastal carbon steel tank samples with nine (9) months of storage under high-humidity conditions examined. The current study offers a systematic correlation between viscosity and elemental contamination for marine distillate fuels under operational storage conditions regarding real-world samples.